gl: remove hard-coded platform to window type mappings
gl: remove hard-coded platform to window type mappings

This should fix compilation on non-Apple Darwin and plausibly addresses
hypothetical future support for Mesa's shared GLAPI.

krichter722/vlc,xkfz007/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,xkfz007/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.2,krichter722/vlc,vlc-mirror/vlc,krichter722/vlc,krichter722/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,krichter722/vlc,xkfz007/vlc,shyamalschandra/vlc,krichter722/vlc,xkfz007/vlc,jomanmuk/vlc-2.2,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,vlc-mirror/vlc,shyamalschandra/vlc,vlc-mirror/vlc,vlc-mirror/vlc,krichter722/vlc,shyamalschandra/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,xkfz007/vlc